It is known to so design mixture metering systems that the proportioning or metering of the fuel takes place according to so-called learning control systems. In this connection, reference can be made to German published patent application DE-OS No. 28 47 021 and British patent No. 20 34 930B. Such a learning control system contains in a permanently active write-read memory, for example, values for the injection which are available during the operation of the engine. By forming such characteristic fields, a quickly reacting precontrol of the injection quantity or generally of fuel metering is provided or also for other operating parameters of the engine suitable for fast changing operating conditions, for instance, ignition timing, exhaust gas recirculation rate, et cetera. Learning adjustment systems can be so designed, for example, that the individual characteristic field values are corrected in dependence upon the operating characteristic values and written into the respective memory.
With respect to the foregoing, it has already been proposed in U.S. patent application Ser. No. 831,476 to structurally influence determined regions of a basic characteristic field via an adaptive precontrol and it has further been suggested to influence each control value obtained from the characteristic field multiplicatively via a global factor, in the sense of a shift of all the characteristic field support points. U.S. patent application Ser. No. 831,476 was filed on Feb. 20, 1986, now U.S. Pat. No. 4,676,215 and is herewith incorporated by reference.
It further has been proposed in U.S. Pat. No. 4,676,215 to change, according to the learning process, the values stored in the characteristic field and selected in dependence upon the operating characteristic quantities of the internal combustion engine, so that not only a single predetermined characteristic field value but also those respective characteristic field values lying in its vicinity can additionally be manipulated in dependence upon the change of the value encountered in each case. U.S. Pat. No. 4,676,215 is herewith incorporated by reference.
In order to be able to introduce a learning process with respect to the precontrol, one needs the characteristic operating quantities, which set up the characteristic field, such as the throttle flap position and the rotational speed. In addition to the characteristic operating quantities, one also needs an actual value indication of the actual operating condition of the internal combustion engine, wherein as the actual value ordinarily the adjustment factor or the control quantity of a lambda-regulator will be evaluated. This control quantity of the lambda-regulator influences therefore in the sense of an adaptive learning the precontrol stage and at the same time serves as a fed-back actual value during the actual adjustment of the mixture control, while establishing the precontrol values from the characteristic field region changed by adaptive learning, as required.
Ordinarily, one will proceed such that the correction factor produced by the lambda-regulator will be averaged, subjected to appropriate boundary conditions, and then incorporated as well into the structural characteristic field superimposed on the basic characteristic field (structural adaptation) and into a global factor (global adaptation). The incorporation takes place in each case on leaving an influence area (adaptation area) defined around each characteristic field support point.
In connection with the adaptive learning processes in the precontrol region for the mixture control of internal combustion engines, it is further known to take into consideration the tank venting control in such internal combustion engines in such a manner that tank venting will be permitted only for certain operating conditions of the engines, and that during this time the adaptation process for the evaluation of the characteristic field is interrupted, that is the mixture adaptation is inhibited. Background with respect to the foregoing is provided in German published patent application DE-OS No. 28 29 958 and in a publication of Robert Bosch GmbH entitled "Motronic"--Technical Bulletin C5/1, August 1981.
The reason for the above is that an active carbon filter, which is associated with the fuel tank and absorbs fuel vapors up to a determined maximum amount, must necessarily be flushed or regenerated during the operation of the motor. This flushing or regeneration occurs in connection with the underpressure developed by the internal combustion engine in the intake region. However, the foregoing results in an additional fuel-air mixture caused by this tank venting. This mixture, as an unmeasured mixture, falsifies the fuel quantity normally determined with high precision and with a complex effort (in the context of fuel injection systems this quantity is determined, for example, by the duration of the injection control command t.sub.i) and the total amount of the fuel introduced into the internal combustion engine which results therefrom.
The lambda sensor utilized as the actual value transmitter evaluates, however, the total amount of fuel in relation to the quantity of air and the fuel introduced per unit of time, so that in the learning adaptation in the precontrol region, which is based on the averaged value of the lambda sensor signal, inaccuracies are introduced if the mixture adaptation is not inhibited during the tank venting phase.
The invention is based on the recognition that in an internal combustion engine other sources of error also exist, which can lead to undesirable and insofar falsifying shifting in the mixture adaptation (structural adaptation and/or global adaptation) so that the task of the present invention is to provide that, in adaptive learning in the precontrol characteristic field region, an interruption of the mixture adaptation is always effected when uncontrollable influences of transitory character occur which influences cause a change of the output signal of the actual-value transmitter (lambda sensor).